Aging data analysis and risk assessment: Development and demonstration study

Abstract

This work develops and demonstrates a probabilistic risk assessment (PRA) approach to assess the effect of aging and degradation of active components on plant risk. The work (a) develops a way to identify and quantify age-dependent failure rates of active components, and to incorporate them into PRA; (b) demonstrates these tools by applying them to a fluid-mechanical system, using the key elements of a NUREG-1150 PRA; and (c) presents them in a step-by-step approach, to be used for evaluating risk significance of aging phenomena in systems of interest. Statistical tests are used for detecting increasing failure rates and for testing data-pooling assumptions and model adequacy. The component failure rates are assumed to change over time, with several forms used to model the age dependence--exponential, Weibull, and linear. Confidence intervals for the age-dependent failure rates are found and used to develop inputs to a PRA model in order to determine the plant core damage frequency. This approach was used with plant-specific data, obtained as maintenance work requests, for the auxiliary feedwater system of an older pressurized water reactor. It can be used for extrapolating present trends into the near future, and for supporting risk-based aging management decisions.

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